Delaminated structure

In exfoliated nanocomposites, delaminated structures are obtained if a large number of polymer chains are present between the layers and the layers stand >10 nm apart. Thus, the interlayer expansion is comparable to the radius of gyration of the polymer rather than that of an extended chain, as in the case of intercalated hybrids [35]. 

Table 1 summarizes the prominent reflections and features that confirm successful swelling and pillaring. The feature that was found diagnostic and indicative of delaminated structure was coalescence of the 101 and 102 peaks,... 

Knit line A visible line seen in a molded polyurethane part that indicates where two flows of reacting polyurethanes have come together and joined. Often caused by flow turbulence, incorrect pour point placement, or poor polyurethane flow. Depending on the severity, the knit line can be a weak point in the molding that may cause future delamination, structural failure, or poor dimensional stability. 

While the IR and MAS NMR spectra are consistent with the delaminated structure of ITQ-2 and ITQ-6, the Argon isotherms represented as a function of log P/P are highly informative on the changes in topologies experienced during delamination (Fig. 3). It can be seen there that ITQ-2 does not show the adsorption corresponding the large 12 MR cavities characteristics of the MWW structure, while preserves that of the intralayer 10 MR circular channels. Meanwhile, in the case of ITQ-6, the adsorption at the 10 MR pores of ferrierite has practically disappeared. 

The mesoporous structure, with high surface area could provide simple accessibility of guest molecules to the active sites and increase their chances to receive light. One research group fabricated mesoporous photocatalysts with delaminated structure. The exfoliated layered titanate in aqueous solution was reassembled in the presence of anatase Ti02 nanosol particles to make a great number of mesopores and increase the surface area of Ti02 [370] (see Table 6). 

Where the loading of nanomaterial is increased, the resistance of nanocomposites towards different chemical media increases. This may be due to the more compact and cross-linked structure of the nanocomposites, along with a reduction of permeability characteristics compared to the pristine system. The delaminated structure of the nanocomposites reduces the permeability and, as a result, the various ions or species present in the different media cannot easily penetrate the surface as they have to follow an indirect path. A significant increase in the thermal degradation temperature and a decrease in the thermal degradation rate have also been observed in most of these nanocomposite systems where there is an increase in the amount of dispersed nanomaterial. This improvement of thermal stability in the nanocomposites systems is related to the well-dispersed nanomaterials, which hinder the diffusion of volatiles and assist the formation of char after thermal decomposition. 

The last one is an exfoliated or delaminated structure where there is complete separation of clay platelets into random arrangements. This is the ideal nanocomposite arrangement but is harder to achieve during synthesis and/or processing. For this successful dispersion organophili-zation is essential for successful exfoliation of hydrophilic clays in most... 

Depending on the nature of the filler distribution within the matrix, the morphology of the nanoeomposites can evolve from the so-called intercalated structure where a regular alternation of the layered silicates and polymer monolayers is observed, to the exfoliated (delaminated) structure where the layered silicates are randomly and homogeneously distributed within the polymer matrix. The easiest and technically most attractive way to produce these types of materials is to knead the polymer in the molten state with a modified layered silicate, such as montmorillonite. Compounding on different machines, such as a Buss ko-kneader or mills, still produces essentially the same morphology in the resulting nanoeomposites. 

Cone calorimetry is used to evaluate the flammability imder flre-like conditions. Relevant parameters such as the rate of heat release (HRR) and its peak value, heat of combustion (He), smoke yield (specific extension area, SEA), and carbon monoxide 5ueld are obtained. Table 2 shows some t5q)ical data for layered silicate nanocomposites based on organically treated montmorillonite, with polyamide 6, poly(propylene-gra -maleic anhydride), and polystyrene as the host matrix. Nanocomposites imder investigation have either delaminated (PAG) or intercalated-delaminated structures. In all cases there is a substantial reduction in peak HRR value (50-75%), whereas He and CO formation show little variation. 

The addition of layered silicate to a polymer can result in three different morphologies formation of micro- (or even macro-) composites, or nanocomposites with intercalated polymer species (where the polymer is sandwiched between 2D silicate nanolayers) or with exfoliated/delaminated structures. In the last case, the 2D silicate nanolayers are completely separated, at least at distances of a few nanometers from one another. 

These materials, unlike the other nanophase materials described in this chapter, are nano-sized in only one dimension and thereby act as nanoplatelets that sandwich polymer chains in composites. Mont-morillonite (MMT) is a well-characterized layered silicate that can be made hydrophobic through either ionic exchange or modification with organic surfactant molecules to aid in dispersion [5,23]. Polymer-layered silicates may be synthesized by exfoliation adsorption, in situ intercalative polymerization, and melt intercalation to yield three general types of polymer/clay nanocomposites. Intercalated structures are characterized as alternating polymer and siHcate layers in an ordered pattern with a periodic space between layers of a few nanometers [13], ExfoHated or delaminated structure occurs when silicate layers are uniformly distributed throughout the polymer matrix. In some cases, the polymer does not intercalate... 

Figure 3.3 shows the mass loss rate data for PS, PS with micro-dispersed sodium-MMT, and PS-MMT (mass fraction 10%) nanocomposite with a mixed intercalated-delaminated structure [for a transmission electron micrograph (TEM), see Figure 3.4a]. The times at which samples were exposed to pyrolysis were 82, 95, 200, 400, and 1150 s. These times correspond to particular events in...

Adsorption studies dealing with liquid systems clearly show the potential use of PILCs as adsorbents for environmental applications. One example is the uptake of toxicants such as chlorophenols on pillared and delaminated clay structures (67). Al-delaminated laponite is more effective in adsorbing pentachloro-phenol (PCP) than the Al-pillared montmorillonite. At an equilibrium time 24 h, an equilibrium pH = 4.7, and an initial PCP concentration of 38 p,mol L , the maximal adsorption of PCP was 27 pimol g on Al-delaminated laponite and 12 xmol g on Al-pillared montmorillonite. The binding of PCP onto the substrate is attributed to interactions between the PCP molecule and the immobilized AI2O3 species. The greater adsorption capacity for the delaminated structure arises from the greato- dispersion and availability of the Al oxide aggregates in the clay. 

Figure 11.1 Different possibilities of layered clay dispersion in a polymer matrix (a) phase separation (b) intercalated structure (c) exfoliated (delaminated) structure.

Beyond this traditional class of polymer-filler composites, two types of nanocomposites can be obtained. Intercalated structures are formed when a single (or sometimes more) extended polymer chain is intercalated (sandwiched) between the silicate layers. The result is a well-ordered multilayer structure of alternating polymeric and inorganic layers. Exfoliated or delaminated structures are obtained when the silicates are completely and uniformly dispersed in the continuous polymer matrix. The delamination configuration is of particular interest because it maximizes the polymer-clay interactions, making the entire surface of the layers available for the polymer. This should lead to the most significant changes in mechanical and physical properties. A schematic of the types of possible structure formations in PC composites is depicted in Fig. 13.2. 

Melt rheological properties of PCL-based nanocomposites were first reported by Krishnamoorti and Giannelis in the case of delaminated structures prepared by in-situ intercalative polymerization. Recently, Lepoittevin et a/. reported the detail melt rheology properties of PCL-based nanocomposites prepared by melt intercalation method. The rheological behaviour of the PCL filled with 3wt.% of MMT-AIk and MMT-(OH)2 was significantly different compared to the unfilled PCL and PCL/MMT-Na nanocomposites, for which the power law observed at low frequencies agrees with expectation for thermoplastics. The frequency dependence of G and G" was, however, perturbed by organically modified MMT. The effect was dramatic in the case of G which drops from 2 to 0.14 and 0.24 for MMT-(OH)2 and MMT-AIk, respectively. 

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